Gary,
I have seen this in 3 homes where light color (white or light neutral) carpet was in a room that was exposed to sunlight. It was just a guess of mine but I told the customer that the gasses that are constantly being released from the pad was trapped in the carpet because of the low, or tight to the floor, furniture. Like I said, it’s just a guess but it makes sense to me and the customer bought it. Sun fadeing of the exposed areas along with no fading of the covered areas could also be the issue. Maybe the carpet originally had a pink tint to it but now it’s faded away. Again, just a guess.